Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

106
FXUS63 KLOT 020526
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1226 AM CDT Thu Jul 2 2026

.KEY MESSAGES...

- Hot and humid conditions will continue through the holiday
  weekend with daily peak heat index values near 100 degrees.

- Waves of thunderstorms are expected Thursday evening through
  the weekend. With that said, there will be many dry hours.

&&

.DISCUSSION...
Issued at 138 PM CDT Wed Jul 1 2026

Tonight and Thursday:

Regional GOES-19 water vapor imagery augmented by RAP analysis
data imagery depicts a quintessential summertime pattern
characterized by a large upper-level high pressure system
(around 596dm) centered over the southeastern United States.
Such a "heat dome" continues to provide hot and humid conditions
in the general region with heat indices around 100 degrees in
the local area at press time. Meanwhile, a recent hand surface
analysis revealed an outflow-reinforced frontal boundary
stretching from central Lower Michigan through central Wisconsin
and through northwestern Iowa. The frontal boundary continues
to serve as a highway for episodic clusters of showers and
storms in the central and upper Great Lakes region, including a
supercell that recently produced a 3 inch hailstone near Fond du
Lac, Wisconsin. This is all to say, the weather outside is
definitely living up to the standards of July.

Have been watching an area of clumping cumulus clouds across
far northeastern Iowa early this afternoon for signs of
initiation into thunderstorms as they approach the
Illinois/Wisconsin state line. With an absence of large-scale
forcing as well as around 100 J/kg of MLCIN noted on the 18Z DVN
RAOB, do not currently expect thunderstorms to emerge out of
the clumping cumulus clouds. However, if the off chance they do
take off, they would be prone to impacting portions of northern
Winnebago, Boone, and perhaps McHenry counties later this
afternoon/evening with a localized threat for damaging winds,
damaging hail, and flash flooding.

With that said, another round of thunderstorms is expected
along the stalled frontal zone across northern Iowa and southern
Minnesota along the nose of a modest southwesterly 850mb low-
level jet. A somewhat uneven overlap of moisture-laden
instability but marginal deep-layer shear will encourage
thunderstorms to evolve into loosely organized outflow-driven
clusters that tend to track into central Wisconsin through the
night. Our area will hence be dry, warm, and muggy tonight with
overnight lows generally in the mid to locally upper 70s.

If convective coverage is relatively high this evening and
overnight across Wisconsin, amalgamation of repeated cold pools
should lead to a southward-drifting region of outflow that would
be prone to spilling into far northern Illinois or perhaps
southwestward off Lake Michigan toward daybreak. Such an
evolution is depicted by both the NAM3/HRDPS, which typically
perform well in these sorts of regimes. Even if outflow does
reach our area tomorrow morning, current thinking is that it
would have minimal impact on hot and humid conditions with highs
expected to soar back into the upper 80s to lower 90s with peak
heat indices of 100 to 105F. Most daylight hours look dry.


Thursday evening into early Friday morning:

By tomorrow evening, the upper-level heat dome will begin to
"flatten" as the frontal boundary stalls from central Iowa
toward the Illinois and Wisconsin border. CAM-based guidance is
fairly consistent in showing an upper-level shortwave riding the
top of the heat dome into the Lower Great Lakes during the
evening hours leading to the development of storms along the
frontal boundary. With forecast soundings depicting minimal
capping by early afternoon, suppose a thunderstorm or two may
develop as early as 4 PM. However, coverage should increase
markedly with the shortwave itself favoring after 7 or 8 PM.
With the trajectory of the shortwave favoring southern
Wisconsin, storms should remain largely north of Interstate 88.
However, if there is a high coverage of storms, can certainly
envision the southward spill of outflow-driven storms toward or
even further south of I-80 by daybreak Friday. Any storm may
produce locally damaging winds or flash flooding tomorrow
evening and night, again favoring areas north of I-88.


Friday through the weekend:

Ensemble model guidance remains in agreement that the upper-
level heat dome will break down Friday and transition toward
somewhat weak but quasi-zonal upper-level flow through the
weekend. With 850mb temperatures remaining somewhat stagnant and
near +20C, will go with a persistence forecast for both heat
and humidity levels with daily peak heat index values near 100
degrees. Subtle upper-level shortwaves embedded within the
quasi-zonal flow (if not just afternoon heating of the boundary
layer) should support episodes of thunderstorms in the area. In
this kind of pattern, any storm can be prone to producing
damaging winds and flash flooding, though moreso on a localized
basis than widespread. With all of that said, many hours should
be dry.

We are very cognizant of the large number of outdoor events and
activities scheduled for the upcoming holiday weekend with
heightened attention on the forecast for the timing and coverage
of thunderstorms. This type of pattern is one where confidence
in timing and location of storms comes much more into focus
about 12 to 24 hours beforehand. So, stay tuned to the forecast.


A note about heat headlines:

Yesterday was definitely the most oppressive day of the ongoing
heat wave. While forecasted heat index and HeatRisk values this
afternoon through the upcoming holiday weekend outside of Cook
County are forecasted to fall well short of local Extreme Heat
Warning criteria (four or more consecutive days with peak heat
index >105F and/or widespread HeatRisk level of 4 out of 4),
will maintain the product across the entire area for the sake of
a consistent message with neighboring forecast offices.

In terms of any extension in heat headlines beyond Thursday, am
not sure we will meet local criteria even for a Heat Advisory
given forecast heat indices are expected to remain below 105F.
With that said, there is something to be said about the
cumulative effect of the heat (as Friday would be day 5 of heat
index values near or above 100F), so future shifts may need to
consider a Heat Advisory anyway for Friday or Saturday
regardless barring, of course, the cooling effects of
thunderstorms.

Borchardt

&&

.AVIATION /06Z TAFS THROUGH 12Z FRIDAY/...
Issued at 1226 AM CDT Thu Jul 2 2026

- Potential short duration wind shift to the northwest prior to
  daybreak.

- Low confidence in any thunderstorm potential.

- Gusty southwest winds this afternoon.

Winds remain out of the southwest and around 10 kt, but gusts
have generally diminished. Wind directions should mostly remain
out of the southwest through the TAF period with diurnally
driven gusts once again in the afternoon. The only exception is
outflow that has developed out of the thunderstorm complex
approaching Milwaukee, WI at the time this discussion was
published. If it were to maintain itself, there could be a
brief wind shift to the northwest prior to daybreak. But a.)
the look of the outflow on radar appears to be weakening and b.)
any wind shift between 10 to 20 knots and for only a short
period. Decided to keep it out of the TAF for now, but may need
to amend as it approaches.

As the upper level ridge that drove this week`s hot and precip
free weather breaks down and shifts east, a more active pattern
for storms will set up through this weekend. However, the
forcing mechanisms to generate storms, at least through the
current TAF period, are too weak to have confidence in exact
timing. Model guidance reflects this uncertainty by showing
little to no agreement. For now, the PROB30 at KRFD was
maintained for the time being, but as the previously mentioned
outflow looks weaker, there is lower confidence anything would
arrive there. Additional chances for storms around the region
are possible late afternoon and during the overnight into
Friday, but with such low confidence at this distance, the TAFs
were kept dry.

DK

&&

.CLIMATE...
Issued at 1246 AM CDT Wed Jul 1 2026

     .Daily Records for the Upcoming Week........

Chicago (KORD)
            Record High       Record Warm Minimum
July 1       103 (1956)            78 (1931)
July 2        99 (1970)            79 (1911)
July 3       102 (1949)            78 (1911)
July 4       102 (2012)            80 (1921)


Rockford (KRFD)
            Record High       Record Warm Minimum
July 1       101 (1931)            76 (1970)
July 2        99 (1910)            74 (1970)
July 3        99 (1925)            75 (2012)
July 4       102 (2012)            77 (1977)

NWS Chicago

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Extreme Heat Warning until midnight CDT Thursday night for
     ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-
     ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-
     ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

IN...Extreme Heat Warning until midnight CDT /1 AM EDT/ Thursday
     night for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...None.

&&

$$

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